Flow reversal in open hearth furnaces and the like



June 23, 1942. K, c, MccuTcHEoN ETAL 2,287,186

I FLow REVERSAL IN OPEN HEARTH FURNACES 'AND THE LIKE Filed Sept. 8,-1939 .6 Sheets-Sheet 1 West 3 EAST I900 Z000 ZIOO INVENTORS. KENNETH C. M Cu reuse/v BY Mum 5 HAND.

ATTORNEYS.

.h'me 23, 1942.

K. c. M CUTCHEON ET AL v 86 FLOW REVERSAL IN OPEN 'HEARTH FURNACES AND THE LIKE Filed Sept. 8, 1959 e Sheets-Sheet 2 EAST Cuzc KER l I I04, I

I900 zo qo 21:90 5a, I 25 z 3X f .233

FIG. 6'.

' INVENTORIS- 4 KENNETH C M- CUTCHEON NO BY MLTE/f E. HA/va.

ATTORNEYS June 23, 1942. cuTH 0 vETAL 287,186

FLOW REVERSAL IN OPEN HEARTH FURNACES AND THE LIKE Filed Sept. 8, 1939 6 Sheets-Sheet 3 ll |II l|lll II l IIIII IIL INVENTORaS- M ..U s m H r0 UN. 0 m w H TA 5 R H wm MW 0 M J1me 1942- K. c. MCCUTCHEON ET AL 2,287,186

FLOW REVERSAL IN OPEN HEARTH FURNACES AND THE LIKE Filed Sept. 8, 1939 6 Sheets-Sheet 4 v WEST 30 E451- EAST CHECKER-L----\ ,1/WEST CHECKER INVENTOR8. KENNETH CI M- f'urc eolv M475 5. HANG. BY q ATTORNEYS.

June 23, 1942. K. c. MCCUTCHEON Ell-AL 2,287,186

FLOW REVERSAL IN OPEN HEARTH FURNACES AND THE LIKE Filed Sept. 8, 1939 e Sheets-Shet 5 Wes-r EAs-r as as l I v I900 z oo b zloo INVENTORS- KEN/very (I MS(UTCI-IEON ATTORNEYAS.

Patented June 23, 1942 QFFICE.

FLOW BEVERSAL IN GPEN HEAR/TH FUR- NACES ANDTHELIKE ration of Ohio Application September 8, 1939, Serial No. 293,998

7 Claims.. (Cl. 236) Thisinvention relates to the reversal of flow in an open hearth or other regenerative furnace. It is generally the practice at the present time to pass the incoming air through a checker chamber into the open hearth furnace where it meets the gas stream. The products of combustion pass through the furnace and out through a checker chamber on the other side. Gradually the preheated air on the incoming end becomes so cold that the flame temperature is too low, and it is then desirable to reverse the direction of flow so that the flame will have the benefit of hot air from the other checker chamher and so that the entering checker chamber will not become too cold. Upon reversal of the flow that checker chamber which had been on the incoming side is now subjected to the prodnets of combustion and is heated up. Thus it is desirable to reverse the flow through the furnace when the desired temperature conditions are reached to obtain the most economical operation.

Reversals have been made in the past:

1. On the basis of the judgment of the skilled operator.

2. After a definite time interval.

3. When a predetermined maximum temperature has been reached.

4. When a predetermined minimum temperature has been reached.

5. When a predetermined difierence in tem perature between the hot end and cold end has been reached.

These methods vary in excellence and in ascending order. The purpose of all these methods has been to maintain as high a preheat of air for combustion as possible at alitimes, both for economy and in order to be able to reach the high temperature necessary to refine molten steel, and to keep the preheat equal on the flame in each end so that melting and refining will proceed equally well from either end,- whereby full economies can be obtained.

The first two methods, where no temperature measurement was made, fail to approach the desired results. Of those methods in which a temperature measurementis made the fifth is the best, but it still fails in the attainment of the highest preheat, because the temperature measurement has of necessity been made in the colder end of the regenerators.

While the present system can be carried out with temperatures measured at any place, and either with temperature measurement by thermocouples or radiation pyrometers, yet it lends itself especially to the use of temperature measurement by means of radiation pyrometers. The drop in preheat to be used is modified by the temperature of the regenerator last used, only in such a way as to maintain a balance between both ends and thus promote the greatest possible economies.

Radiation pyrometers cannot be operated on difference in temperatures as set up by two opposing circuits in connection with a recording instrument, and base metal couples cannot be made to last in the hot end of checkers. Temperature drop systems lend themselves to use with radiation pyrometers, which are better for use in hot places.

According to this invention the reversal is made upon a predetermined drop in temperature of the incoming air so measured by a ther mocouple, radiation pyrometer, or aspirating thermocouple located in the furnace ends, uptakes, checker chambers or flues. In other words, assuming that at the time of reversal the temperature of the incoming air is say 2000 degrees the next reversal will be made when the temperature of that air has dropped a predetermined amount, as for, example, 200 degrees. minimum temperature of that air is not definite but represents a floating value depending upon what was the maximum temperature at the time of reversal. In connection with this method if the system tends toward an unbalanced condition, a compensation is made which prevents the system from becoming unbalanced.

. The actual reversal of flow which involves switching the gas supply from the burner on one end of the furnace to the burner on the other end of the furnace and also the opening and closing of a number of ducts whereby to change the flow of the products of combustion and air from one direction to the other, may be accomplished automatically if desired, or manually. If it is manually accomplished it is desirable to provide a signaling system whereby the operator is warned that a reversal should be made.

Thus the primary object of the invention is to provide for reversal upon the attainment of a predetermined drop in temperature of the preheat on either side of the regenerative system. A second function is to modify the schedule of reversal based on the first function so that the temperatures of the two sides do not diverge too widely or become unbalanced.

These and other objects of our invention which will be described more in detail hereinafter or which will appear to those skilled in the art Thus the upon reading these specifications, we accomplish by that arrangement and series of method steps of which we shall now describe an exemplary embodiment.

Reference is made to the drawings forming a part hereof and in which:

Figures 1, 2, 3, 4, and 6 represent schematic diagrams of an' open hearth furnace with its associated checker chambers, and showing a circult arrangement for indicating when a reversal should :be made, andfor preventing unbalance in the system.

Fig. 7 is a detail perspectiveview of a portion of an instrument used and Fig. Bis an elevational view of the same showing the three positions thereof.

Briefly in the practice of this invention, we utilize a two-point recording controller having a motor operated table. An instrument of this type is disclosed in a patent in the name of T. R. Harrison, 1,946,280 issued February 6, 1934. This instrument is arranged to record or control temperatures at two points, as shown in Figs. 12 to 16 of the patent. We modify this instrument in that the shaft described in the above mentioned patent on page 4, lines to 45 and shown at B in Fig. 14 is provided with an electric motor drive for rotation in either direction at low speed. The rotation of the shaft B engaging in the thread groove B (Fig. 17) provides for setting the control table A upon completion of an electric circuit through the motor in one direction or the other An interrupter of any desired type such for example, as a mercury switch is placed in the electrical circuit to-each of the motor windings. As shown in Figs. 1 to 6 of this application at M and N, these switches are preferably connected together mechanically to make and break at the same time as by means of a connecting link Ill. The switches may be operated in any convenient way to given an adjustable period of contact and this may be accomplished for example by means of a cam driven by the main shaft 12 shown in the-figures of the Harrison patent above mentioned. We prefer to arrange the switches to have a period of contact of from one to fifteen seconds in each fifteen seconds, and ordinarily we prefer to have the switches make contact for a per each seven seconds of switch contact a control table movement representing about five degrees F. a

The control table A of the Harrison patent is modified by the substitution of a piece I0a (see Figs. 7 and 8) for the member a shown in Figs. 9, 10, and 11 of the patent. The member- Illa is made of such a length that an edge Ila is exposed beyond the member 5a which is equal to the length occupied on the chart of the instrument by the number of degrees of desired drop in preheat of the regenerative system. For example, if it is desired to have a reversal take place upon a 200 degree dropin temperature the member Ila is made to extend beyond the member So by an amount which on the chart scale would represent 200 degrees.

The switches W and Z are of the mercury and lass type and are arranged to close one circuit in one position and another circuit in the opposite position while leaving both circuits open when the switch is in the neutral or horizontal position. The switch W is operated by the instru-' ment from the indication of temperature by the ated in accordance with the relation of the actualtemperature at the moment to the position of the element 23c in its relation to the members 5a and Ila.

The part 230 is as in the Harrison patent a projection from the recording'carriage. In actual operation the member Illa is set' so that the exposed portion I la is equal to the required drop in preheat temperature.

The operation of this portion of, the instrument is,,as follows: Assuming that a reversal from east to west checker incoming has just been made and that the part 230 is at aposition under the member Ila adjacent to 5a, as long as the member 23c is opposite the portion Ila the respective switch W or Z is in a, horizontal position and-both circuits will open. As the temperature of the checker drops the member 23c in time assumes a position outside of Ila as indicated at 231: in Fig. 8. When this happens the switch W is actuated to low position. Similarly if the member 230 occupies the position shown at 231 in Fig. 8, the switch is thrown to high position.-

Referring now to Figs. '1 to 6 inclusive, the open hearth furnace is shown at 30; the west checker chamber is shown at 3| and the east checker chamber at 32. The burners are shown at 33 and 34 and the thermocouples at 35 and 36. The control table is indicated at 31, while the arrows 38 and 39 represent respectively the edge of the member 5a and the edge of the member Ila. The control table drive motor is shown at 40 and a portion of a chart is shown at M. 42 represents a double-pole, double-throw switch and 43 is a main line switch. A signal station is shown at 44 and includes a green light Gr, a white light Wh, and a red light R, as well as a bell B.

The operation of the system will now be described using -an exemplary set of conditions. In Fig. 1 the condition is illustrated where the west checker is cooling and the east checker is heating and the flow of gases is in the direction of the arrows, that is from west to east. The doublepole, double-throw switch 42 is in the upper position and since the temperatures of both checkers shown on the chart at't and t are between the points 38 and 33, the switches W and Z are in closing the switches M and N, and the control table 31 is therefore stationary. In the illustration it is assumed'that the predetermined drop in temperature is to be 200 degrees and that at this particular time the range is from 1900 to 2100 degrees. In this situation none of the lights are lit and the bell is not ringing, and this represents the general condition during-a cycle.

Referring now to Fig. 2 the situation is illustrated where the west checker has cooled the predetermined 200 degrees, and it is time for a reversal to be made but the reversal has not yet been made. It will now be observed that the temperature t of the west checker has dropped just below the position of the arrow 38 indicative of the edge of the member 5a in Figs. '7 and 8, so that the switch W is shown thrown into the low position. This establishes a circuit through the green and the white lights and the bell. so that both-the green and white lights are illuminated and the-bell'rings. Also an enabling cir- The white light and The operator now accomplishes the reversal by directing the fuel flow through the gas line 34 and shutting off the line 33, and by operating the dampers to change the flow of gases through the furnace and by throwing the switch 42 to the opposite position. The operation of throwing the switch 42, either manually upon the reversal of the furnace or by automatic means at the same time, efiects the disconnection of the control mechanism as such from the one thermocouple, and effects its connection to the thermocouple in the checker chamber which becomes the incoming checker chamber in the cycle just starting.

The situation which now obtains is illustrated in Fig. 3 and it will be noted that the lights are now off and the bell has ceased ringing. However, since the control table had moved down scale as shown in Fig. 2, the temperature t of the east checker is now above scale with respect to the arrow 39. Therefore the situation is as represented at 23y in Fig. 8 and the switch Z is now shown in high position. This sets up a. circuit in the opposite direction through the motor 40 so that upon contact being made by the switches M and N the motor All will turn in the opposite direction and will move the control table 31 up scale by small increments until the point 39 just passes the temperature 15'.

The description thus far shows the operation of the system as long as an unbalanced condition does not exist. Figs. 4 to 6 illustrate the operation when an unbalanced condition does 38 and 39, i. e. in the position indicated at 232 in Fig. 8, so that both switches W and Z are in neutral position.

InFig. 5 there is shown the situation just before reversal at the end of'the cycle shown about to start in Fig. 4. The east checker which is now the cooling checker has cooled down but before it has cooled down the predetermined 200 degrees its temperature it passes the control point 38 thereby causing the control table 31 to start moving down scale by virtue of the fact that the switch W has been thrown to low position. In this situation it will be noted that the white light is lit indicating that a reversal should be made and the bell is ringing as a warning signal, and that the red light is lit indicating that the west checker has heated up and is now to become the preheating checker.

In Fig. 6 the condition is shown when the reversal has been made after the situation of Fig. 5. The double-pole, double-throw switch 42 has been thrown to the opposite position and on account of the fact that the temperature t of the west checker is above the control point 39 it will be understood that immediately upon reversal the temperature t of the west checker begins to fall and when the temperature t and the control point 39 pass, the control table will stop and will not move farther up scale. It will also be noted that the lights andbell have been turned off.

It will thus be seen that the double-pole, double-throw switch 42 serves to block out of operation those control circuits not involved in the control of temperature of that side of the regenerative system which at the time is preheating, and it will be observed that the motorized control table serves to modify the preset drop in preheat temperature and thus serves to prevent the two sides of the system from becoming unbalanced.

As will be evident from the drawings and the foregoing description, what we mean by a condition of furnace balance is a condition in which, during repeated cycles, the checker work on the outgoing furnace end heats up to substantially the same temperature as the checker work on the incoming side had at the start of the cycle, so that repeated furnace reversals occur at the same temperatures for the incoming side and the same temperatures for the outgoing side. By a condition of unbalance in the furnace we mean a departure from these conditions, such for example as would obtain if the reversals took place when the incoming checker chambers in alternate reversals differed markedly as to starting temperatures.

Under conditions of furnace balance the movements of the control table up or down will offset or counterbalance each other. Under conditions of furnace unbalance, there will be a net movement of the control table in the one direction or the other produced by a higher than normal or lower than normal temperature of the incoming checker work at the start of a cycle. This will tend to compensate the instrument for such departures from normal, and will tend to cause the instrument to signal the operator or automatically to eiTect-furnace reversal upon the attainment of the predetermined drop in temperature of the checker work on the incoming side during any one cycle, irrespective of any difference between the actual starting temperature of the incoming side during this cycle and the temperature on the incoming side during the last cycle.

But as we have indicated, the control table is arranged to have -a relatively slow movement, and preferably this movement is by increments with time intervals therebetween (through the action of the switches M and N). The control instrument itself is solely under the influence of the conditions in the incoming checker work, and these conditions as will be evident, tend to produce movement of the control table only during a time when the actual incoming temperature lies outside the range of temperature covered by the table in its then position. Thus the compensation referred to above is never instantaneously and completely accomplished. For this reason.,the compensation which we effect, instead of tending to perpetuate and make permanent a condition of furnace unbalance, tends over a number of cycles to bring the furnace into a condition of balance as nearly as the actual construction of the furnace and the exigencies of furnace operation will permit.

While we have spoken of the temperature of the checker work, We have done so for convenience, having pointed out above that the mode of measurement of conditions at the incoming end of the furnace is not a limitation on our invention, and that the thermo-couples, pyrometers, or other temperature sensitive instruments may be variously located; and in the claims which follow we refer to the temperature of the air at the incoming end of, the furnace meaning thereby to include all indexes of the temperature conditions at the incoming end of the furnace whether the actual measurement be taken of the air, the checker work, the chambers, uptakes, fiues, or other criteria.

It will be understood that numerous modifications will occur to those skilled in the art and we therefore do not intend to limit ourselves except as pointed out in the claims which follow.

Having now fully described our invention what we claim as new and desire to secure by Letters Patent, is: j

1. In combination with a regenerative open hearth furnace having checker chambers, a two point recording controller, having recording means operatively connected alternately with temperature responsive devices in said checker chambers, whereby a continuous record is made of the conditions in each checker chamber, a

' reversing mechanism for said open hearth furnace, a control table in said recording controller demarking a predetermined temperature drop, means in said recorder for energizing a circuit when the temperature conditions in the entering checker chamber have attained a predetermined temperature drop, said means being independentof the means for recording the temperature conditions in the other checker chamher, a motor drive for said control means, and means for energizing said motor drive when the initial temperature in the entering checker chamber passes beyond a maximum or minimum control point as established by a previous position of said control table.

2. In combination with a regenerative open hearth furnace having checker chambers, a two point recording controller, having recording means operatively connected alternately with temperature responsive devices in said checker chambers, whereby a continuous record ismade of the conditions in each checker chamber, a reversing mechanism for said open hearth furnace, a control table in said recording controller demarking a predetermined temperature drop, means in said recorder for energizing a circuit when the temperature conditions in the entering checker chamber have attained a predetermined temperature drop, said means being independent of the means for recording the temperature conditions in the' other checker chamber, a motor of the conditions in each checker chamber, a reversing mechanism for said open hearth furnace, a control table in said recording controller demarking a predetermined temperature drop, means in said recorder for energizing a circuit when the temperature conditions in the entering checker chamber have attained a predetermined temperature drop, said means being independent of the means for recording the temperature conditions in the other checker chamber, a motor drive for said control means, and means for energizing said motor drive when the initial temperature in the entering checker chamber passes beyond a maximum or minimum control point as established by a previous position of said control table, said means for energizing said motor drive including means for confining the energization thereof to interspaced time intervals whereby said control table is prevented from being instantly and completely responsive to the temperature of the air passing through the said entering checker chamber, said last mentioned means including a pair of switches, each of said switches being controlled'by the temperatureresponsive element in one of said checker chambers but only during the time when the said checker chamber is an entering checker chamber, whereby said control table will be intermittently driven in one direction or another depending upon the position of the switch controlling it, and a switch to shift the control of said motor from one of the aforementioned switches to the other upon reversal of the flow in said furnaceJ 4. The method of operating a regenerative furnace which comprises selecting as a basis of furnace reversal a definite temperature drop in the air entering the furnace from its temperature at the start of a cycle to the point of reversal, reversing the furnace upon the attainment of said temperature drop of the air entering the furnace from its temperature at the start of each cycle, during conditions of furnace balance, and varying said temperature drop during conditions of furnace unbalance in such manner as to tend to re- "store conditions of furnace balance.

5. The method of operating a regenerative furnace which comprises selecting as a basis of furdrive for said control means, and means for, en- I ergizi'ng said motor drive when the initial temperature in the entering checker chamber passes beyond a maximum or minimum control point as established by a previous position of said control table, said means for energizing said motor drive including means for confining the energization thereof to interspaced time intervals whereby .said control table is prevented from being inchambers, whereby a continuous record'is made nace reversal a definite temperature drop in the air entering the furnace from its temperature at the start of a cycle to the point of reversal, reversing the furnace upon the attainment of said temperature drop of the air entering the furnace from its temperature at the start of each cycle, during conditions of furnace balance, and varying said temperature drop during conditionsof furnace unbalance in such manner as to tend to restore conditions of furnace balance while continuously recording the temperature conditions ateach end of said furnace.

6. The method of operating a regenerative open hearth furnace which comprises determining the times of reversal from cycle to cycle on the basis of conditions at the entering end of said furnace, and during conditions of furnace bal-# ance effecting reversal upon the attainment of a predetermined and constant dropin temperature of the air at said incoming end from its temperature at the start of the cycle terminated by the said reversal, and during conditions of furnace unbalance, effecting at least partial compensation for differences in temperature of the incoming air at the start of successive cycles.

7. The method of operating a regenerative open hearth furnace which comprises determining the times of reversal from cycle to cycle on the basis of conditions at the entering and of said furnace, and during conditions of furnace balance effecting reversal upon the attainment of a predetermined and constant drop in temperature of the air at said incoming end from its pensation for difierences in temperature of the incoming air at the start of successive cycles said compensation, however, being made to be incomplete whereby to tend to restore conditions of 5 furnace balance over a plurality of cycles.

KENNETH c. MCCUTCHEON. WALTER E. HAND. 

